Loudspeakers form a major part of family audio and video entertainment systems. The loudspeakers, currently, fall into the following two categories: two-channel high fidelity (Hi-Fi) stereo speakers and multi-channel home theater speakers. Hi-Fi stereo speakers are used to listen to music. Most users of Hi-Fi stereo speakers are fans of music or audio equipment, and thus always emphasize on sound quality of music from Hi-Fi stereo speakers. While Hi-Fi stereo speakers output high fidelity music and a pleasant sound, most Hi-Fi stereo speakers partially lack a sense of immediacy and exhibit poor dynamic behavior at low frequency ranges of audio signals and thus provide an unsatisfactory experience while watching a movie. Multi-channel home theater speakers are used for watching movies. These multi-channel home theater speakers do not meet the demand of fans who prefer good sound quality when listening to music from the multi-channel home theater speakers and watching movies simultaneously.
At present, the multi-channel home theater speakers developed have 7.1 channels or more channels and a subwoofer driver that typically reproduces substantially low frequency band audio signals, and have attracted very few purchases because of the disorder created by installation of 8 or more speakers of the 7.1 or more channel home theater speakers in households. In general, users do not choose high fidelity (Hi-Fi) speakers for multi-channel home theater systems due to cost considerations. Often households that have installed the multi-channel home theater speakers discard the multi-channel home theater speakers after a short span of use since the multi-channel home theater speakers fail to offer Hi-Fi music to movie viewers. Thus, there is a need for a speaker system that reproduces audio signals of a wide range of frequencies with enhanced sound quality for watching movies and listening to music.
Most of the conventional loudspeakers comprise two or more speaker drivers that fit into an enclosure, for example, a cuboid shaped box in a vertical direction. A frequency divider in a conventional loudspeaker divides the audio signals to be reproduced by each of the speaker drivers based on frequencies of the audio signals. Such an enclosure forms a sound baffle for speaker drivers that may damage the tone and quality of the sound reproduced due to the limitation of the enclosure geometry and the material used to build the enclosure. Furthermore, sound quality degradation may be caused due to diffraction interferences among different sound frequencies on a baffle of a speaker driver and standing waves present in the enclosure. The non-uniformity of the material used to build the enclosure may also contribute the sound quality degradation. For example, a wooden material used to build the enclosure typically contains cracks and defects resulting in the sound quality degradation. Hence, there is a need for a speaker system that produces high quality audio sound of a wide range of frequencies without intrinsic sound degradation due to the interferences from possible standing waves in the enclosure and the frequency diffraction interferences from the baffle.
In general, a sound field from a conventional speaker system with a box enclosure typically forms a directional sound cone with a narrow solid angle along a central axis of the conventional speaker system. This narrow solid angle would squeeze a sweet spot in the middle of two or more speaker drivers of the conventional speaker system. A small lateral shift from the sweet spot shifts the whole auditory scene in the direction of the shift and for a listener off to the side, the scene collapses near one of the speaker drivers, and little is heard from the other speaker driver. Hence, there is a need for a speaker system that reproduces audio signals of wide range of frequencies without directivity.
In general, the sound signals in the middle frequency range to the high frequency range present more directivity due to their relatively short wavelength. Therefore, implementing a point sound source, that is, a speaker driver without a baffle, for the middle frequency range to the high frequency range requires a substantially small speaker driver to reduce its directivity. In general, if a speaker driver is placed in the middle of a space without any baffle, the sound wave produced by the speaker driver would be canceled out due to the opposite phases of the sound wave in the front and in the back of the speaker driver, thereby creating a sound wave short-circuit. On the other hand, a large speaker driver is normally required to reproduce the sound signals in the lower frequency range. Due to the longer wavelength at lower sound frequencies, large size of the large speaker driver will not result in directivity as in the mid sound frequency range to high sound frequency range. Hence, there is a need for a speaker system that produces a point sound source effect without using a baffle.
A majority of the sound speaker systems do not a adopt point sound source design. The PLUTO speaker system from Linkwitz Lab is an example of a floor-standing loudspeaker system to implement a point sound source speaker system. This loudspeaker system uses a forward-playing broadband speaker driver, a 2 inch full range driver, and an upward-playing woofer with a 5.25 inch diameter. The upward-playing woofer strengthens bass effect of the forward-playing broadband driver at low audio frequencies, which is installed on top of a vertically closed cylinder. A dynamic electronic frequency cross-over is configured and a four-channel audio frequency amplifier for such a loudspeaker system is implemented. The loudspeaker system creates a good point sound source characteristic with a substantially good sense of immediacy and dynamic behavior for the sound reproduction at multiple sound frequencies. The original designs of the Pluto series speaker systems from the Linkwitz Lab were provided to music lovers as do it yourself (DIY) projects with an unprecedented sound field effect. However, due to the limitation for the selection of the primary components from the design, the frequency response range was merely, for example, about 60 Hertz (Hz) to about 15000 Hz, which is less ideal for a requirement for a real high fidelity sound system. The Pluto speaker system utilizes electronic frequency division or preceding stage frequency division, with a set of specially designed power amplifiers to form an active speaker system. Such a speaker system is incompatible to connect with other external power amplifiers, and therefore the degree of freedom of selection of the external power amplifiers, a richer tone change, and listening experiences provided to the users are limited.
Hence, there is a need for a speaker system that reproduces audio signals of a wide range of frequencies and exhibits behavior of a point sound source without using a baffle. Moreover, there is a need for a speaker system comprising drivers molded on waist drum shaped enclosures using an alloy metal material to avoid interferences from the possible standing waves and resonance oscillations in the speaker system. Furthermore, there is a need for a speaker system that is compatible for connection to different external power amplifiers for usage flexibilities.